DDL、DML、DCL、DQL相关操作
DDL (数据库定义语言)#
数据库的创建以及删除
create database mysql_test;
drop database test;
表的创建 (create)、修改 (alter)、重命名 (rename)、删除 (drop)
创建表
create table s_emp(
id int primary key,
last_name varchar(20),
dept_id int);
create table s_dept(
id int primary key,
name varchar(20));
表s_emp是员工表,表s_dept是部门表,但是之间没有设置外键联系
修改表属性,具体看alter用法
alter table s_emp add constraint 'fk' foreign key(dept_id) references s_dept(id);
实际上等同于
create table s_emp(
id int primary key,
last_name varchar(20),
dept_id int,
constraint 'kf' foreign key(dept_id) references dept_id(id));
外键(表级约束)
DML (数据库操控语言)#
插入数据 (insert)、更新数据 (update)、删除 (delete)
insert into s_dept values(1,"web"),(2,"bigData"),(3,"php"),(4,"java");
insert into s_emp values(1,"lisi",1),(2,"wangwu",1),(3,"zhangsan",2),(4,"jake",3);
insert into s_emp(id,last_name) values(5,"birup");
update s_dept set name="hadoop" where id = 1;
替换
把update换成replace即可
delete from s_emp where id=4;
DCL (数据库控制语言)#
具体看MySQL用户密码及权限修改笔记
DQL (数据库查询语言)#
等值连接
select e.id as id,last_name as name,name as dept_name from s_emp e,s_dept d where e.dept_id = d.id;
左外连接
select s.id,s.last_name,s.dept_id,d.id,d.name from s_emp s left outer join s_dept d on s.dept_id=d.id;
select s.id,s.last_name,s.dept_id,d.id,d.name from s_dept d left outer join s_emp s on s.dept_id=d.id;
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